1. Field
The following embodiments of relate to a Medium Access Control for Wireless Networks.
2. Description of the Related Art
Wireless networks, such as a Wireless Local Area Network (WLAN) according to the IEEE 802.11 standard, are widely deployed, and typically provide the benefits of low cost, simple deployment, and high speed data communications. In a WLAN, the physical layer of IEEE 802.11a/b/g/n standards is typically used to transmit and receive data packets over a shared wireless medium. The IEEE 802.11 standard's Medium Access Control (MAC) typically provides a reliable delivery mechanism for user data over wireless channels which may be subject to interference and fading. IEEE 802.11 standard's DCF (Distributed Coordination Function) is a typical MAC protocol based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), in which a handshaking mechanism is typically used to combat the effects of collisions and facilitate transmission of large data packets. In such a DCF scheme, when a source node is ready to transmit a packet, the source node first monitors the activity on the transmission channel until an idle period equal to a DIFS (Distributed Inter Frame Space) is detected. In this instance, the source node waits for another random backoff interval before transmitting to avoid a collision with other nodes. The source node starts the transmission by sending a RTS (Request-To-Send) control packet. If the control packet is received correctly, the destination node sends a CTS (Clear-to-Send) control packet after a SIFS (Short Inter Frame Space) interval. Once the CTS packet is received, the source node transmits its data packet after an SIFS interval. If the data packet is received correctly, the destination node responds by sending an acknowledgement (ACK) packet after the SIFS interval. IEEE 802.11 DCF also makes use of a network allocation vector (NAV) for virtual carrier sensing. The NAV is typically maintained by nodes that are not currently involved in any transmission or reception of packets, and tracks the remaining time of any ongoing data transmission and updates according to information received in the control/data packets.
With the expanding use of wireless mesh networks employing ad-hoc routeing between nodes via other nodes which are used as relay nodes, MAC schemes such as IEEE 802.11 DCF have been extended to so called cooperative MAC schemes that allow cooperation between nodes at the MAC layer to enable routeing via beneficial multi-hop routes, so that, for example, a slow single hop transmission may be replaced by a fast two or more hop transmission. MAC protocols for cooperative communications include CoopMAC (Cooperative MAC), rDCF (relay enabled DCF), and Robust Cooperative Relaying.
However, conventional cooperative MAC protocols can be inefficient in terms of complexity, signalling overhead, and data capacity. For example, a database of the signal qualities of links between nodes may have to be maintained, with associated signalling, in order to select an appropriate multi-hop route. Furthermore, conventional cooperative MAC protocols can be restricted in their capabilities by a need to limit interference between simultaneous transmissions of data. As a result, selection of routes can be mutually exclusive due to potential interference and thus limit achievable bandwidth.
Therefore, mitigation of these and other problems with such systems is needed.